Here are the two quick steps you need to take to find which WordPress version your theme is running on:
1. Log in to your WordPress admin panel.
2. In the Dashboard, search for a panel At a Glance. In this panel, you’ll be able to find which WordPress version you are using and under which theme.
Bear in mind that if you can’t find this panel, it means that it is hidden. To view the panel, click on Screen Options in the top right corner, and a header section will expand. Check the option At a Glance, and the panel will appear.